Emergency vehicle warning devices for use in automobiles to detect the presence of an emergency vehicle such as an ambulance or fire engine are well known in the art and numerous patents have issued covering various systems. In spite of the vast amount of prior art in this field, there has been little if any use of such devices by the average automobile owner. The primary reason for this lack of enthusiasm comes down to the cost of the item to the individual. In order to avoid false triggering of the device by outside sounds other than an emergency vehicle sound such as a siren, the circuits involved must discriminate carefully and as a result such circuits as have been available have been fairly expensive.
In order that a vehicle warning device be readily acceptable, it is essential that the cost be kept to an absolute minimum so that the average owner can readily afford to purchase the device and use it in his car. However, attempts to skimp on electronic circuitry design in order to produce a cheap or inexpensive package have always heretofore resulted in an inferior product which is susceptible to false triggering.